CS50_week4 Memory
原创
CS50_week4 Memory
原创
greatak
修改于 2024-09-23 01:26:43
修改于 2024-09-23 01:26:43
代码可运行
运行总次数：0
代码可运行
关联问题
换一批
int n = 50;
pointer 变量占 8bytes
string s = "HI!";
#include <stdio.h>
#include <cs50.h>
int main(void)
{
string s = "HI!";
printf("%p\n", s);
printf("%p\n", &s[0]);
}
s是string "HI!"的指针；那么s[0], s[1], s[2]...组成的array s也是指针？
#include <stdio.h>
#include <cs50.h>
int main(void)
{
string s = "HI!";
printf("%p\n", s);
printf("%p\n", &s[0]);
printf("%p\n", &s[1]);
printf("%p\n", &s[2]);
printf("%p\n", &s[3]);
}
![每个元素s[i]只占一个byte](https://developer.qcloudimg.com/http-save/yehe-11230753/d831ff9a7d1d9f348ec2fa9075d8d62e.png)
每个元素s[i]只占一个byte
string s = "HI!"; char *s = "HI!";string s ↔ char *s 等效
#include <stdio.h>
int main(void)
{
char *s = "HI!";
printf("%s\n", s);
}
typedef uint8_t BYTE;typedef char *string;pointer arithmetic
#include <stdio.h>
int main(void)
{
char *s = "HI!";
printf("%c", *s);
printf("%c", *(s + 1));
printf("%c\n", *(s + 2));
}
s[1] ↔ *(s + 1) compiler translate it as
#include <stdio.h>
#include <cs50.h>
int main(void)
{
string s = get_string("s: ");
string t = get_string("t: ");
if (s == t)
{
printf("Same\n");
}
else
{
printf("Different\n");
}
}
char *s = get_string("s: ");
char *t = get_string("t: ");
string s = get_string("s: ");
string t = s;
t[0] = toupper(t[0]);
printf("%s\n", s);
printf("%s\n", t);
#include <cs50.h>
#include <stdio.h>
#include <ctype.h>
#include <string.h>
#include <stdlib.h>
int main(void)
{
char *s = get_string("s: ");
char *t = malloc(strlen(s) + 1);
for (int i = 0, n = strlen(s); i <= n; i++)
{
t[i] = s[i];
}
if (strlen(t) > 0)
{
t[0] = toupper(t[0]);
}
printf("%s\n", s);
printf("%s\n", t);
}
char *s = get_string("s: ");
char *t = malloc(strlen(s) + 1);//memory allocate
if (t == NULL)//not enough memory available
{
return 1;
}#include <cs50.h>
#include <stdio.h>
#include <ctype.h>
#include <string.h>
#include <stdlib.h>
int main(void)
{
char *s = get_string("s: ");
if (s == NULL)
{
return 1;
}
char *t = malloc(strlen(s) + 1);//memory allocate
if (t == NULL)//not enough memory available
{
return 1;
}
strcpy(t, s);
if (strlen(t) > 0)
{
t[0] = toupper(t[0]);
}
printf("%s\n", s);
printf("%s\n", t);
free(t);//opposite of malloc，释放memory
}
NULL is the adrress zero.
valgrind
#include <stdio.h>
#include <stdlib.h>
int main(void)
{
int *x = malloc(3 * sizeof(int));
x[0] = 72;
x[1] = 73;
x[3] = 33;
free(x);
}
int main(void)
{
int *x;
int *y;
x = malloc(sizeof(int));
*x = 42;
*y = 13;
y = x;
*y = 13;
}
y没有assign a value， so y maybe 0, or 1000, or etc.
*y就到了某个不知道的memory的地方。
passing by reference
#include <stdio.h>
int main(void)
{
char s[4];
printf("s: ");
scanf("%s", s);
printf("s: %s\n", s);
}
File I/O
#include <cs50.h>
#include <stdio.h>
#include <string.h>
int main(void)
{
FILE *file = fopen("phonebook.csv", "a");
if (file == NULL)
{
return 1;
}
char *name = get_string("Name: ");
char *number = get_string("Number: ");
fprintf(file, "%s,%s\n", name, number);
fclose(file);
}#include <stdio.h>
#include <stdint.h>
typedef uint8_t BYTE;
int main(int argc, char *argv[])
{
FILE *src = fopen(argv[1], "rb");
FILE *dst = fopen(argv[2], "wb");
BYTE b;
while(fread(&b, sizeof(b), 1, src) != 0)
{
fwrite(&b, sizeof(b), 1, dst);
}
fclose(dst);
fclose(src);
}#include <stdio.h>
int main() {
int num = 1;
printf("%03d\n", num); // 使用%03d格式化输出，表示至少打印3位，不足的前面补零
return 0;
}原创声明：本文系作者授权腾讯云开发者社区发表，未经许可，不得转载。
如有侵权，请联系 cloudcommunity@tencent.com 删除。
原创声明：本文系作者授权腾讯云开发者社区发表，未经许可，不得转载。
如有侵权，请联系 cloudcommunity@tencent.com 删除。
评论
登录后参与评论
暂无评论
推荐阅读
相关推荐
C/C++ 文件与指针操作笔记
更多 >一站式MCP教程库，解锁AI应用新玩法
涵盖代码开发、场景应用、自动测试全流程，助你从零构建专属AI助手
腾讯云开发者
